Class-D audio amplifiers are switch mode amplifiers that switch at a high frequency to produce a rectangular waveform at the amplifier's output. Class-D amplifiers may be much more efficient that linear audio amplifiers, and as a result may employ smaller power supplies and eliminate heat sinks. Accordingly, class-D amplifiers may significantly reduce overall system costs, size, and weight relative to linear amplifiers of equivalent power.
Some class-D amplifiers use a pulse width modulator (PWM) to generate pulses that vary in width with the audio signal's amplitude. The pulses may switch output transistors of the amplifier at a fixed or variable frequency. Some class-D amplifiers may rely upon other types of pulse modulators, such as pulse density modulators. The rectangular waveform generated by the class-D amplifier is filtered to remove the high-frequency carrier waveform and reconstruct the audio waveform, which can be used to drive a speaker and produce sound.
Some class-D amplification systems include circuitry to model and monitor speaker performance. Such systems use the speaker performance information to optimize amplifier output and protect the speaker. These amplification systems may be referred to as “smart amplifiers.”